This invention generally relates to monomers and methods for preparing them. Polycarbonate resins prepared with the monomers and capacitors comprising the polycarbonate resins are also provided.
Because of their transparency, toughness and relatively low cost, polycarbonates are useful in a wide variety of applications and are produced globally on a scale of well over a billion pounds annually. But one example of an industrially important use of polycarbonate is in the manufacture of capacitors.
Over the last decade, significant increases in capacitor reliability have been achieved through a combination of advanced manufacturing techniques and new materials. Greatly enhanced performance has been obtained particularly in so-called film capacitors. Film capacitors can be classified into three types based on the manufacturing technology, namely, film and foil capacitors, metallized film capacitors and mixed technology film capacitors.
Generally, metallized film capacitors consist of two metal electrodes separated by a layer of plastic film. The metallized plastic film is constructed by vacuum depositing metal film onto a layer of plastic film. This would offer compact capacitor structure, self-clearing capability, longer lifetime, and higher energy density. Some of the commonly used plastic films are polypropylene and polyester films. The metal film layer is typically extremely thin, in the order of about 50-500 angstroms and is typically aluminum or zinc or alloys of such. Compared to other types of capacitors, metallized film capacitors have advantage in size, simplicity, and cost of manufacturing, and hence been widely used in the power electronics industry.
While significant improvements have been made in metallized film capacitors, certain issues, such as thermal stability and reduced lifetime continue to present challenges to their widespread adoption. For example, polycarbonates made from phosgene and BPA have been used in the past for the manufacture of thin film capacitors, as have polypropylene and certain polyesters. However, the glass transition temperature of these materials (generally speaking, 150° C. or lower) limits the continuous-use, working temperatures of articles made from these resins to only about 120° C. or less. Furthermore, the low dielectric constant (about 2.9 @ 1 MHz, for polycarbonate resins) of these resins limits the stored energy of capacitors made from these materials to about 1 Joule/cc.
New polymeric resins would thus desirably be provided, having higher dielectric constants, and capable of operating at operating temperatures in excess of 120° C. Such resins would be expected to be useful in a wide variety of articles, including thin film capacitors, and metalized thin film capacitors in particular.